Transponder tags and the use of a mobile telephone for locating objects carrying such transponder tags are well known. For example, WO 2006/092220 A2 describes a method for preventing the loss of keys that are connected to an RFID transponder tag. If the user loses/misplaces his keys, he can review the stored location information and with the knowledge of the most recently known location the user has a good chance to retrieve the lost keys. The power supply for the RFID transponder tags is provided by an RFID signal, which is wirelessly transmitted from the mobile telephone to the RFID transponder tag.
Also, WO 2014/177984 A2 describes an RFID-enable mobile telephone that is used for detecting correspondingly tagged objects. In contrast thereto, US 2011/0260839 A1 uses tags with an energy-harvesting circuit and the mobile telephone communicates with the tag according to a WLAN or Bluetooth communication protocol.